With the advance of medical science, the demand for platelet concentrates with low contamination of white blood cells (WBC), such as, lymphocytes is rapidly growing. Platelets are fragments of a large cell located in the marrow called a megakaryocyte. Platelets have no nucleus and are primarily responsible for hemostasis, although they also have a role in tissue healing. They interact to chemicals released from damaged endothelial cells by becoming "sticky" and adhering to the damaged tissue. Platelets then release ADP, a chemical, which causes other platelets to stick to each other. This action, also known as aggregation, forms the primary white clot. Platelets then activate plasma proteins responsible for clotting which produce the "red" clot or the stable clot. Platelets have a half-life of 4-6 days in the normal adult. Normal platelet counts are 150,000-400,000/mm.sup.3 in the adult. Platelet counts under 20,000/mm.sup.3 can result in spontaneous bleeding.
With the improvement in cancer therapy patients are requiring increased platelet support. In addition, with the large number of screening tests employed for blood products, the number of units that are acceptable are less than in past years. The donor pool is reduced and therefore, the supply of random donor platelets must be conserved.
Procedures for collection of specific blood components from a single blood donor, apheresis, is proven to be a satisfactory approach to cover the demand for blood components. Recently, the equipment for collection of platelets has been directed towards maximizing the yield of pure platelets. (See for example, U.S. Pat. No. 4,416,654.) Today, it is understood that the contamination of platelet concentrates by WBC can lead to medical complications, such as graft-versus-host reactions.
Current blood separation equipment for the collection of platelet concentrates are not sufficient for automatically collecting an optimum pure platelet concentrate.
Accordingly, there is a continuing need for an apheresis separation apparatus and method for automatically collecting platelet concentrates with low white blood cell contamination while maximizing platelet yields.